ABSTRACT

In the last years,Teraherz (THz)-technology has developed to become a powerful tool for non-destructive material investigation (Bäumer 2002, Hoffmann et al. 2005, Mansner et al. 2007). Tomographic information as well as spectroscopic information can be deduced from experimental results of THz-Time Domain Spectroscopy (THz-TDS) by the runtime and spectrum of electromagnetic picosecond THz pulses. Such pulses can be generated by high acceleration of free electrons in a semiconductor. The free electrons are produced by photoelectric effect due to femtosecond laser irradiation. A voltage of about 100V applied to electrodes on the semiconductor with a small distance in the micron range generates a strong electric field in the case of an Auston Switch emitter (Dorney et al. 2000, Shur 2005). For the acceleration of electrons, internal fields at the semiconductor surface (photoDember effect) can be used as well. Figure 1 shows a scheme of an experimental setup for THz-TDS. The spectrum of the picosecond THz-pulse (Fig. 2a) can be calculated by Fourier transformation (Fig. 2b).